1. Field of the Invention
Embodiments of the invention relate to a nonvolatile memory device. More particularly, embodiments of the invention relate to a nonvolatile memory device using a variable resistive element and an associated operation method.
2. Discussion of Related Art
Next generation nonvolatile memory devices are being developed for use in portable consumer products to provide high capacity and low power consumption. These memory devices include, for example, PRAMs (Phase change Random Access Memory) utilizing phase-change material such as a chalcogenide alloy that can be switched between two states, RRAMs (Resistance Random Access Memory) employing material having a variable resistance characteristic of complex metal oxides, and MRAMs (Magnetic Random Access Memory) utilizing the resistance change of MTJ (Magnetic Tunnel Junction) thin films according to the magnetization state of a ferromagnetic substance. The resistance value is maintained in these devices even when no current or voltage is supplied demonstrating nonvolatile memory characteristics.
For example, the phase change material used in a phase change memory cell changes into a crystal state or amorphous state by cooling after heating. The phase-change material in the crystal state has a low resistance defining set data (0) and the phase-change material in the amorphous state has a high resistance defining reset data (1). In order to operate the phase change multiple voltage levels for example, 1.5, 3, 4, and 5 V are needed. A driving-voltage-generating circuit generates these multiple driving voltages by utilizing an external supply voltage as an input. However, if a driving voltage (for example, a boosting voltage) generated by a particular driving-voltage-generating circuit is significantly used in a short period of time, the driving voltage level may be instantaneously dropped. As a result, malfunctions may be introduced into the circuit using this driving voltage inside the phase change memory device.